1. Field of the Invention
This invention relates to disk drive suspensions insensitive to windage encountered in a disk drive that produces track misregistration (TMR) errors. More particularly, the invention relates to disk drive suspensions provided with curvilinear covers over windage sensitive features to provide suspensions having reduced track misregistration errors caused by windage within the disk drive. Windage is the combination of airflow factors acting on a suspension as hereinafter explained. The invention suspension and method block windage airflows from contact with suspension beam surface features that, in windage contact, induce tracking error-causing perturbations in the suspension. The invention uses an airfoil profile-defining deflector that overlies the beam surface features and deflects windage airflows past these features smoothly.
2. Description of the Related Art
One of the critical dimensions of a disk drive is its track density, which is a measure of its ability to correctly write and then read back a very narrow cylinder of data (“track”) in close proximity to other similar, parallel tracks. Current disk drives have a track density of 100 thousand tracks per inch or more, which means that the track-to-track centerline distance (“track pitch”) is 10 millionths of an inch or less. The suspension must hold the recording head in correct position over the track well within this distance or the head will erroneously read data from or write data onto another track, resulting in incorrect or lost data. The measure of the disk drive's inability to hold position correctly is known as “off track error”, or track misregistration. The track density figure is on an increasing trend over time with a corresponding decrease in track pitch in order to obtain increased disk storage capacity in each successive new disk drive generation.
Improving suspension natural resonance frequencies and amplitudes has the effect of removing the influence of the peaks of the frequency response function that is a major contributor to off track error. The natural frequency responses are excited or driven by vibrations inherent in the disk drive, including motor vibration for the motor that spins the disk, bearings in the motor spindle and actuator, and the lateral acceleration of the spinning disks and accompanying air flows (or windage) over, under, across, head-on and otherwise into and around the suspension. Other than windage-related sources these contributors to error have been addressed with some success.
The graph of the relationship between the amplitude response of the suspension and the excitation frequency is a transfer function referred to as FRF or Frequency Response Function. A transfer function is the output (response) divided by the input (excitation). The FRF is normally determined by shaking or vibrating the base of the suspension and measuring the amplitude of the resulting movement of the slider at the other end. This will reveal the peak amplitudes and their corresponding frequencies. In actual use in the disk drive, however, as opposed to the test stand, the excitation is provided by the actuator (during seek, which is lateral movement to move from track to track) and by the airflows (collectively generalized as windage) in the disk drive. The total off track error is characterized by the area under the windage function.